This invention relates to a polymeric coating which inhibits the adhesion of ice to the surface of an object. The invention further relates to the composition and method of making a polysiloxane(amide-ureide) which provides a durable, long-lasting, anti-ice coating when applied to a substrate.
The everyday buildup of ice upon the surfaces of mechanical, physical, and natural objects is a familiar annoyance, and quite often a safety hazard. The slick layers of ice that form on highways, driveways, and walkways make transportation difficult. The masses of ice that accumulate within or upon industrial, agricultural, or other mechanical equipment make operation of the equipment difficult or impossible. And, the weight of ice that weighs upon power lines, buildings, and signs often causes damage to those structures.
Ice accumulation upon vehicles, such as air or marine vehicles, poses a challenging problem. For example, ships traveling in the arctic and other cold climates may have ice form thereon, thereby disadvantageously increasing the weight and decreasing the maneuverability of the ships.
Buildup of ice upon the wings and components of an aircraft is of particular concern. The lift generated by the wings, and thus the ability of the aircraft to become and remain airborne, is dependent on the shape of the wings. Even a small accumulation of ice upon the surface of the wings can significantly increase drag and dramatically reduce lift. Further, ice buildup along control surfaces of the aircraft can impede the movement of those surfaces and prevent proper control of the aircraft.
There are a large variety of techniques used to control the buildup of ice upon the wings and other surfaces of aircraft. For instance, the aircraft may be deiced before takeoff by radiant heat energy or by application of a chemical spray which melts the ice from the wings. Such deicing sprays are environmental hazards. The ritual of deicing is well known to airline passengers traveling through cold environments.
Another method of deicing aircraft includes providing flexible pneumatic coverings (bladders) along the leading edges of the wings, and supplying bursts of air or fluid to expand the flexible coverings to break away any overlying ice. Similarly, bleeding air from the aircraft engine and routing the heated air to the surface of the wing heats the wing and melts the ice. Finally, ice may be removed from the wing by providing high-current pulses of electricity to a solenoid disposed within the wing which causes the wing to vibrate, fracturing any accumulated ice.
Although the previously mentioned methods of ice removal are generally effective, they require the continuous supply of air, chemicals, or electrical power in order to rid the wing of its burden. It would be preferred, of course, to prevent the accumulation of ice in the first place, but past attempts to develop practical passive methods of ice prevention have failed.
One would expect that known non-stick coatings would be able to prevent ice from adhering to the surfaces which they coat. In fact, aluminum surfaces coated with a polytetrafluoroethylene material exhibit a zero break force between the ice and the polytetrafluoroethylene coating. However, upon repeated freezing, the favorable properties exhibited by polytetrafluoroethylene and similar coatings degrade, resulting in a coating with little or no anti-icing capacity.
What is needed is a durable surface coating with long lasting anti-icing and/or de-icing properties which does not require the continuous supply of air, chemicals, or electrical power in order to rid a surface of ice or prevent ice from forming upon the surface. What is further needed is a surface coating that may be easily applied to the surface, especially to an aircraft, and which retains its functionality under a variety of environmental conditions, such as those typically encountered by a commercial or military aircraft. What is further needed is a method of applying the surface coating to at least a portion of a vehicle, such as an aircraft.
The invention is a polysiloxane(amide-ureide) coating capable of inhibiting the accumulation of ice upon the surface of a substrate, a process of producing the polysiloxane(amide-ureide), and a method of coating vehicles, particularly aircraft, with the polysiloxane(amide-ureide) coating. The polysiloxane(amide-ureide) forms a durable, long lasting, anti-ice coating when employed upon a substrate. When coated upon a substrate, the polysiloxane(amide-ureide) coating disrupts bonding between the ice and the coated substrate. Moreover, when ice does form, the coating disrupts the hydrogen bonding between the ice and the coated surface, thereby diminishing the ability of the ice to adhere to the surface. The ability of the coating to adhere to surfaces, and the ability of the coating to inhibit the formation of ice upon coated surfaces, makes the polysiloxane(amide-ureide) particularly useful for inhibiting the formation of ice on aircraft or other vehicles. The polysiloxane(amide-ureide) has the general formula: 
wherein
R1 and R2 are independently selected from the group consisting of C1 to C10 alkyls, aryls, and polyaryls;
R3 and R4 are independently selected from the group consisting of hydrogen, C1 to C6 alkyls, aryls, C3 to C6 cycloaliphatics, and C3 to C6 heterocycles;
A1 and A2 are independently selected from the group consisting of hydrogen, C1 to C6 alkyls, aryls, polyaryls, C3 to C6 cycloaliphatics, and C3 to C6 heterocycles, and are preferably methyl;
wherein the alkyls may be linear or branched, saturated or unsaturated, halogenated or non-halogenated; aryls are preferably selected from C6, C10, and C14 aryls and may be substituted or non-substituted, including alkylaryls and halogenated aryls; polyaryls are two or more aryls linked by at least one carbon-carbon bond and are preferably selected from biphenyl and terphenyl; cycloaliphatics may be saturated or unsaturated, halogenated or non-halogenated; heterocycles may be saturated or unsaturated, halogenated or non-halogenated; and alkylaryls may be linear or branched, saturated or unsaturated, halogenated or non-halogenated;
x is a number from 1 to 1000, preferably between about 200 and 500; and,
Y is selected from a substituted dicarboxyl residue and a diisocyanate residue wherein preferably about 40% to about 60% of the Y component within the polymer is the substituted dicarboxyl residue and the remaining portion of the Y component within the polymer is the diisocyanate residue, and wherein preferably greater than about 50% of the Y components are non-linear. It is the combination of both the dicarboxyl residues and the diisocyanate residues in the same polymer backbone that gives the desirable properties relative to interchain strength and ice inhibiting properties.
A preferred polysiloxane(amide-ureide) is represented by the formula: 
wherein each of R1, R2, A1, A2, R3, R4, and x are as defined above, and Z is a dicarboxyl residue and CYAN is a non-linear diisocyanate residue.
The polysiloxane(amide-ureide) is formed by reacting a diamine-terminated polysiloxane, a halide substituted dicarboxylic acid, and a diisocyanate. The beginning diamine-terminated polysiloxane has the general formula: 
wherein R1, R2, R3, R4, A1, A2, and x are as defined above.
The halide substituted dicarboxylic acid is a low molecular weight xcex1,xcfx89-dicarboxlic acid wherein the hydroxyl from each carboxylic acid component has been replaced with a halide constituent, typically chloride, and where the dicarboxylic acid may be as long as a 10 carbon dicarboxylic acid. At least a portion of the substituted dicarboxylic acids are preferably selected from unsaturated acids, such as fumaryl, succinyl, phthalyl, terephthalyl and maleyl halides, and more preferably fumaryl chlorides and maleyl chlorides.
To prepare the preferred polymer, excess amine-terminated polysiloxane is first reacted with a dicarboxylic halide to form a polyamide trimer intermediate. The intermediate is reacted with a diisocyanate to form the polysiloxane(amide-ureide) of formula (Ib). Use of fumaryl halides, phthaloyl halides, and maleyl halides as the dicarboxylic acid halides and use of the non-linear diisocyanate result in a polysiloxane(amide-ureide) with a decidedly non-linear orientation. Thus, the resulting polymer (Ib) contains functional amide groups, functional urea groups, and is amorphous rather than crystalline in nature, due to the non-linear orientation of the polymer molecules. Each of the amide functionality, the urea functionality, and the non-linearity of the polymer improve the polymer""s strength or anti-icing properties. Furthermore, the amide/urea moieties create crystallinity within the polymer via intermolecular hydrogen bonding which, in conjunction with the amorphous nature of the polysiloxane and the non-linearity of the diacid or diisocyanate, create a toughened polymer with enhanced physical properties.
The polysiloxane(amide-ureide) forms a durable, continuous coating when applied to a surface of a vehicle, such as the aluminum or titanium skin on the external surface of an aircraft. The polysiloxane(amide-ureide) also forms a suitable coating layer when applied to a painted surface or to composite structure such as resin matrices containing graphite, carbon, or glass fibers. Aircraft, ships, and other vehicles coated with the polysiloxane(amide-ureide) remain relatively free of ice. If ice does form upon the coated surface, adhesion of ice to the surface is minimal, such that the ice is removed from the surface by any slight application of physical force. The coating is particularly useful to coat the lift and control surfaces of an aircraft to prevent or slow the formation of ice on these surfaces. The coating is also particularly useful for coating the inlets of aircraft to prevent the accumulation of ice on the inlets.
Any ice that does form tends to fall off under the aerodynamic conditions related to operation of an aircraft. Airplanes coated with the polysiloxane(amide-ureide) have improved handling and safety characteristics under conditions which make the surfaces of the airplane otherwise susceptible to icing.
Similarly, ice that forms on other surfaces, such as the roof of a car or the smooth surface of a building, is easily removed by shearing action.